home brew rapid prototype machines

I have a little experience with the rapid prototyping machines. The
problem with these machines is that the parts they create aren't good
for anything but looks and fit testing. You would have to seriously be
in to product development to justify the cost.
The powdered machines (SLS) produce the "best" parts, but they are
still not that strong. The powder can be nylon or an assortment of
other stuff (wax, etc.) but has to be very specific and expensive. I
used SLS parts "as is" for an intake manifold on a motorcycle, that
worked pretty good.
The bulk temperature of the plastic powder has to be accurately
maintained at about 1-2 deg. below the melting temp. The laser just
provides the extra 'kick" to go over the melting point. The two
machines we used required a "butt load" of electricity for the thermal
control stuff and a big 500 gal. tank of liquid nitrogen out back.
When I worked at (big fat company, no name dropping) we had several
of the UV liquid machines and one of the "toothpase" extruder machines.
They were used very little and hardly justified the cost. Mostly the
rapid prototyping stuff was contracted out.
The biggest point missing is the fact that you really need some
powerful 3D CAD software to really get any performance out of the the
rapid prototyping machines. "Po Boy" 3D CAD is about 5K if you pay
retail.
To sum up, I think home shop rapid protoyping machines are several
years away, and even if you could build one, what would you do with it?